So here in this video we're going to take a look at physical changes and how they can affect the overall change in our entropy. Will it increase our entropy or decrease our entropy? So here we're going to say that entropy change, which is ΔS, is a measure of the increase or decrease in disorder due to physical or chemical changes. Now we're going to say an increase in the entropy change is due to an increase in molecular degrees of freedom. So the more movement a substance has, the greater the change in entropy can be.

Now here we're going to say the greater the degree of freedom, which is molecular motion, this is going to cause the greater the change in entropy. So here, let's take a look at change in entropy when it comes to physical changes. All right, so here we have our three major states of matter: solid, liquid, and gas. We can say that our entropy increasing means ΔS goes up. So how can we play around with temperature and pressure to cause this change?

Well, we want more motion, more molecular motion, and we should know that at higher temperatures, molecules absorb the external energy and use it to move themselves even more. So increasing our temperature can lead to an increase in our entropy, our change in entropy. What about pressure? Well, if we have our substances within a container with a movable piston, if we push down on that piston, we're increasing the pressure inside of the container. This would cause molecules to come closer and closer together. They're going to become less disordered, because disorder means you're out and about moving anywhere you want. Increasing the pressure stops that.

So if we want to increase entropy, we want to decrease our pressure, giving the molecules more space, more freedom of movement. Now here, how do we decrease the change in entropy? By doing the exact opposite. If we want to decrease entropy, we force molecules closer together, become more organized. This would happen at higher pressures. And then how do we force molecules to come closer together? We decrease the temperature, so decreasing the temperature would force them to come closer and closer together.

Think of gaseous water. Lower the temperature enough, it will condense down into a liquid. Liquids have way less freedom of motion than gases, right? So keep in mind these changes that we can do in terms of temperature and pressure and how they can affect our entropy change.